FIG. 7 shows a prior art gas jet shooter of the above-defined type for use in a non-contact tonometer.
The gas jet shooter has a rotary solenoid 1 having an arm 2 connected to a piston rod 4 integral with a piston 3 which is mounted in a cylinder 5. A compression chamber 6 is defined within the cylinder 5, which is communicated with a nozzle 7 secured to a head L. The nozzle 7 is to be directed toward the subject eye. The rotary solenoid 1 will, when energized with an electric current, turn the arm 2 in the clockwise direction; the arm 2 will turn back to the original position under the elastic action of a spring (not shown) upon deenergization of the rotary solenoid. An exhaust port 8 is formed in the lower portion of the cylinder 5 for allowing the exhaust of air from the compression chamber 6 in the initial phase of the compressing process.
In operation, the piston 3 is driven upward with the piston rod 3 by energizing the rotary solenoid 1 to turn the arm 2 in the clockwise direction, whereby the pressure in the compression chamber 6 is made higher and the compressed high-pressure air from the compression chamber is shot against the subject eye 9 through the nozzle 7. The tonometer having the gas jet shooting device incorporated therein will make a measurement in a known manner while the air jet is thus shot against the subject eye.
Upon completion of the air jet shooting operation, the rotary solenoid 1 is deenergized to return back to the original position under the elastic action of the spring (not shown) and the piston 3 is moved downward accordingly. Thus, the pressure in the compression chamber will lower and air is drawn into the compression chamber 6 from around the subject eye 9 through the nozzle 7.
The air drawn into the compression chamber 6 after the air shooting operation may carry foreign particles such as dust born in air, or tear particles scattered into air by the air jet, which would be shot together with the air against the subject eye in the next air jet shooting operation. The prior art device is thus disadvantageous from the point of view of hygiene.